High-frequency duplex signaling system



Dec. 25, 1928. 1,696,566

E. F. CARTER HIGH FREQUENCY DUPLEX SIGNALING SYSTEM Filed Nv. 25, 1924 Hill! Inventor Emmett, F. Carter;

His Atndrneg.

Patented Dec'. 25, 1928.

UNITED STATES EMMETT F. CARTER, OF SCEENEC'IADY, NEW YORK, ASSIGNOR TO GENERAL ELEG- TRIO COMPANY, A CORPORATION OF NEW YORK.

HIGH-FREQUENCY DUPLEX SIGNALING SYSTEM.

Application filed November 25, 1924. Serial No. 752,243.

My present invention relates. to signalin systems adapted for duplex operation, and more particularly to high frequency signalin%systems of the carrier current type.

" ne of the objects of my invention is to provide a system whereby duplex operation may be carried onby the use of a single high frequency for the carrier currents transmitted in both directions.

Anotherobject of my invention is to rovide a transmitting apparatus which wi 1 be operative only when a signaling potential is impressed thereon. 7

Still another object of my invention is to provide means whereby both a transmit-ting apparatus and a sensitive receiving apparatus may be simultaneously coupled to a signaling circuit without injury'to the receiving apparatus when the transmitting apparatus is in operation.

The novel features which I believe to be characteristic of my invention are pointed out with particularity in the appended claims; my invention itself, however, both as to its organization and method of operation will best be understood by reference to the following description taken ,in connection with the accompanying drawing in which I have shown diagrammatically one circuit organization which may be used in carrying my invention into efiect.

I have indicated in the drawing the application of m. invention to a duplex carrier current te ephone system for communication over a power line .1. The transmit-v ting apparatus com rises a three-electrode electron discharge tu e 2, which serves as an,

oscillation generator, an amplifying tube 3, which serves tov amplify the oscillations produced by tube 2, a modulating tube 4, which serves to-modulate the amplified oscillations .of tube 3, an amplifying tube 5 for amplifying speech currents produced by telephone transmitter 6 and supplying the amplified speech currents to the input or control circuit of modulator 4, and a control tube 7 for controlling the operation of oscillator 2. The necessary potentials required for operating the different tubes of the transmitter are supplied by a double commutator generator 8 which furnishes two different voltages. The lower voltage is supplied to the plates or anodes of tubes 2 and 5, and the higher voltage to the plates or anodes of tubes 3 and 4..- Tube. 7 is connected in series with the first syllable of the conversation.

the plate feed of oscillator tube 2. The grid of tube 7 is biased by means of battery 9 to a negative potential of such value that the current supplied to the plate circuit'of oscillator 2 is normally insuflicient to perwt of the production of oscillations.

The output from speech amplifier .tube 5 1s supplied to two transformer secondaries 10 and 11, the first of which is included in the grid circuit of control tube 7 and the second of which is included in the grid circuit of modulator tube 4.' When an audio frequency signalin I potential is thus im pressed on the gri circuit of control tube 7 the grid potential becomes less negative, permitting current to be supplied to the oscillator in suificient amount to produce oscillations. The oscillations produced are supplied by the coupling condenser 12 to the grid circuit of power am lifier tube 3 and the amplified oscillations w ich are modulated by means of tube 4 are supplied through a coupling coil 13 to a resonant link circuit 14.

Modulated oscillations are supplied from the link circuit 14110 the power line 1 by means of coupling condensers 15. The action of.

the apparatus in initiatin the supply of modulated oscillations to the signal circuit is substantially instantaneous so that a distant listener does not lose even a fraction of This action is much more rapid than could be obtained by means known in the art, as for example, by controllin the heating of the filament of the devices 7 or 2 in response to voice waves. It will-be noted that the control of the oscillator in response to the si nal currentsis independent of the catho e heating current of'any of the electron dis-- charge devices in the system. c,

A receiving tube 16 having an input cir cuit 17 tuned to the same frequency as that of the oscillations transmitted is coupled to a series tuned link circuit 18, which in turn is coupled to the link circuit 14 by coupling coil 19.- To protect the receivin tube 16 from the effect of otentials whic may be impressed thereon y the transmittin apparatus when the latter is in operation I ,provide in shunt to the link circuit 18 a path which offers a substantially infinite impedance to the received currents and a Comparetively low impedance to currents impressed upon the link circuit 18 from the transmitting apparatus. This device consists of an electron discharge tube 20 having its anode made slightly negative by a battery 21. When signaling currents are being received the impedance of tube 20 is practically infinite. Hence the operation of the receiving system is not interfered with in any Way. When, on the other hand, the transmitter is operating and a high voltage is impressed upon the link circuit 18 the anode of tube 20 will become positive and consequently its impedance will be greatly reduced. As a result a large portion of the energy impressed upon the link circuit will be shunted through tube 20, ,thus partially detuning the link circuit and increasing its impedance and thereby greatly reducing the potential which will be impressed upon receiving tube 16. By this expedient I have found that the receiving tube will be eiiectively protected from injury and that it will always be in condition to receive and indicate received signals as soon as the transmitting apparatus has ceased operation.

While I have shown and described only the apparatus required for one end of a duplex signaling circuit it will of course be understood that the apparatus at the opposite end may be an exact duplicate of that shown and described. It will also be apparent that the system shown and described may be adapted to any form of high frequency signaling desired either over wire lines or by radio and for telegraphic signaling as well as telephonic.

What I claim as new and desire to secure by Letters Patent of the United States, is

1. The combination in a high frequency Y signaling system'of a signaling circuit having normally inoperative transmitting apparatus including electron discharge devices and receiving apparatus simultaneously coupled thereto,'said receiving apparatus being tuned to respond to currents of the frequency supplied to the signaling circuit by the transmitting apparatus, and the transmitting apparatus being so arranged that it supplies high frequency current to the signaling circuit independently of the cathode heating current of any of said discharge devices and substantially simultaneously with the application of signalling potential thereto, and means operating independently of signaling potentials for protecting said receiving apparatus from injury due to the current supplied from said transmitting apparatus.

2. The combination in a high frequency signaling system of a signaling circuithaving transmitting apparatus including electron discharge devices and receiving apparatus simultaneously coupled thereto, said receiving apparatus being tuned to respond to currents of the frequency supplied to the signaling circuit by the transmitting apparatus, said transmitting apparatus comprising a normally inoperative electron discharge oscillator and means operable inde pendently of the cathode heating current of any ofsaid electron discharge devices wher by said oscillator is substantially instantaneously rendered operative by the application of a signaling potential thereto.

3. A transmitting apparatus for a high frequency signaling system comprising an electron discharge oscillator having included in its plate circuit a three-electrode electron discharge device having its potential normally of such value that the current flowing in the plate circuit of the oscillator will be insufiicient to permit of the production of oscillations, and means responsive to a signaling potential for controlling the grid potential thereby to increase the current in the plate circuit sufficiently to permit of the production of oscillations.

4. A transmitting apparatus for a high frequency signaling system comprising an electron dischargeoscillator having included in its plate circuit a. three-electrode electron discharge device having its grid potential normally of such Value that the current flowing in the plate circuit of the oscillator will be insuflicient to permit of the production of oscillations, and means for impressing a signaling potential upon the grid of the electron discharge device and thereby permitting the plate current of the oscillator to increase sufliciently to permit of the production of oscillations.

5. The combination in a high frequency signaling system of a signaling circuit having transmitting apparatus including electron discharge devices and receiving apparatus simultaneously coupled thereto, said receiving apparatus being tuned to respond. to currents of the frequency supplied to the signaling circuit by the transmitting apparatus, said transmitting apparatus comprising an electron discharge oscillator having a plate circuit which includes an impedance of such value that normally no oscillations will be produced and means for substantially instantaneously lowering the value of said impedance in response to a signaling potential suliiciently to permit the production of oscillations, said means operating independently of the cathode heating currents of any of the discharge devices in said transmitting apparatus.

6. The combination in a high frequency signaling systemof a signaling circuit having transmitting and receiving apparatus simultaneously coupled thereto, said receiving apparatus being tuned to respond to currents of the frequency supplied to the signaling circuit by the tran m' sing a? paratus, said transmitting app prising a vacum tube oscillator havi" plate circuit which includes at impecconsisting of an electron discharge device having a continously heated cathode which is so adjusted that the normal current flowing in the plate circuit of the oscillator will be insufficient to permit the production of oscillations, and means res onsive to a signaling potential for subs antially instantaneously'causing an increase in the plate current sufficient to" permit the production of oscillations.

7. The combination in a high frequency signaling system of a signaling circuit having transmitting and receiving apparatus simultaneously coupled thereto, said receiving apparatus being tuned to respond to currents of the frequency supplied to the signaling circuit by the transmitting apparatus, said transmitting apparatus comprising an electron discharge oscillator having included in its plate circuit a three-electrode electron discharge device having its grid potential normally of such value that the current flowing in the plate circuit of the oscillator will be insufficient to permit of the production of oscillations, and means responsive to a signaling potential for increasing the current in the plate circuit sufliciently to permit of the production of oscillations.

8. The combination in a high frequency signaling system of a signaling circuit having transmitting and receiving apparatus simultaneously coupled thereto, said receiving apparatus being tuned to respond to currents of the frequency supplied to the signaling circuit by the transmitting apparatus, said transmitting apparatus comprising an electron discharge oscillator having included in its plate circuit a threeelectrode electron discharge device having its grid potential normally of such valve that the current flowing in the plate circuit of the oscillator will be insuflicient to permit of the production of oscillations, and means for impressing a signaling potential upon the grid of the electron discharge device and thereby permitting the plate current of the oscillator to increase sufliciently to permit of the production of, oscillations.

9. The combination in a high frequency signaling system of a transmitting apparatus comprising an electron discharge oscillator, an electron discharge amplifier for amplifying the oscillations produced by said oscillator, a three element electron discharge control device for controlling the operation-of said oscillator, an electron dis- 0 arge modulator for modulating the amplified oscillations, and signaling means for dering the oscillator operative to produce oscillations and modulating the amplified oscillations. 4

11. The combination in a high frequency signaling system of a signaling circuit having transmitting and receiving apparatus simultaneously coupled thereto, said receiving apparatus being tuned to respond to currents of the frequency supplied to the signaling circuit by the transmitting apparatus, and means for protecting said re-' ceiving apparatus from injury due to the current supplied from said transmitting apparatus, said protective means compris-\ ing a device which offers a high impedance to potentials of the order of magnitude to which said receiving apparatus is intended to respond, and a comparatively low impedance to potentials supplied by the transmitting apparatus.

12. The combination in a high frequency signaling system of a signaling circuit having transmitting and receiving apparatus simultaneously coupled thereto, said receiving apparatus being tuned to respond to currents of the frequency supplied to the signaling circuit by the transmitting apparatus, and means for protecting said receiving apparatus from injury due to the current supplied from said transmitting apparatus, said protectin means comprising a shunt connected e ectron discharge device having its anode at a small negative otential'with respect to its cathode wherey it has a high impedance when the transmitting apparatus 1s not operating and a comparatively low impedance when the transmitting apparatus is operating.

In witness whereof, I have hereunto set my hand this 21st day of November, 1924. EMMETT F. CARTER. 

